Conway suggests avoiding package variables completely,
because they expose your internals to other packages.
Never use a package variable when a lexical variable will suffice.
If your package needs to keep some dynamic state,
consider using an object or closures to keep the state private.

This policy assumes that you're using strict vars so that naked variable declarations are not package variables by default.
Thus,
it complains you declare a variable with our or use vars,
or if you make reference to variable with a fully-qualified package name.

In practice though, its not really practical to prohibit all package variables. Common variables like $VERSION and @EXPORT need to be global, as do any variables that you want to Export. To work around this, the Policy overlooks any variables that are in ALL_CAPS. This forces you to put all your exported variables in ALL_CAPS too, which seems to be the usual practice anyway.

There is room for exceptions. Some modules, like the core File::Find module, use package variables as their only interface, and others like Data::Dumper use package variables as their most common interface. These module can be specified from your .perlcriticrc file, and the policy will ignore them.